Chapter 1 - Foundations for Algebra - 1-2 Order of Operations and Evaluating Expressions - Practice and Problem-Solving Exercises - Page 13: 28

$30$

Substituting $s=4$ and $t=8$, the given expression, $ 3st^2\div(st)+6 ,$ evaluates to \begin{array}{l}\require{cancel} 3(4)(8)^2\div(4\cdot8)+6 \\\\= 3(4)(64)\div32+6 \\\\= 12(64)\div32+6 \\\\= 768\div32+6 \\\\= 24+6 \\\\= 30 .\end{array}